Fuel properties estimation for internal combustion engine

ABSTRACT

Fuel properties estimating apparatus for an internal combustion engine includes a controller to determine an estimated component concentration of a component in a fuel. The controller calculates an air-fuel correction quantity in accordance with an actual air fuel ratio of the engine; and calculates an air-fuel ratio sensitivity correction quantity from the air-fuel ratio correction quantity and a fuel properties correction quantity calculated from a most recent value of the component concentration. The controller then determines a new value of the estimated component concentration in accordance with the air-fuel ratio sensitivity correction quantity.

BACKGROUND OF THE INVENTION

The present invention relates to fuel properties estimating apparatusand process for an internal combustion engine.

A vehicle known as flexible fuel vehicle (FFV) can run on a blend fuelof alcohol and gasoline as well as on gasoline. Alcohol fuel requires alarge amount of fuel injection as compared to gasoline to obtain a givenequivalence ratio because of the different number of atoms of C(carbon). Therefore, an engine system as shown in a Published JapanesePatent Application Publication No. H05(1993)-163992 (pages 1˜4, and FIG.5) is arranged to sense an alcohol concentration with an alcoholconcentration sensor provided in a fuel tank or to estimate the alcoholconcentration from an average value of air-fuel ratio feedbackcorrection coefficient in the case of a failure of the alcoholconcentration sensor.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide fuel propertiesestimating apparatus and/or process for estimating properties of fuelmore accurately and quickly.

According to one aspect of the present invention, a fuel propertiesestimating apparatus for an internal combustion engine, comprises: acontroller to determine an estimated component concentration of acomponent in a fuel for the engine, the controller being configured; tocalculate an air-fuel correction quantity for correcting a fuel supplyquantity for the engine, in accordance with an actual air fuel ratio ofthe engine; to calculate a fuel properties correction quantity inaccordance with a most recent value of the component concentration; tocalculate an air-fuel ratio sensitivity correction quantity from theair-fuel ratio correction quantity and the fuel properties correctionquantity; and to calculate a new value of the estimated componentconcentration in accordance with the air-fuel ratio sensitivitycorrection quantity.

According to another aspect of the invention, a fuel propertiesestimating process comprises: calculating an air-fuel correctionquantity for correcting a fuel supply quantity for the engine, inaccordance with an actual air fuel ratio of the engine; calculating afuel properties correction quantity in accordance with a most recentvalue of the component concentration; calculating an air-fuel ratiosensitivity correction quantity from the air-fuel ratio correctionquantity and the fuel properties correction quantity; and calculating anew value of the estimated component concentration in accordance withthe air-fuel ratio sensitivity correction quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an engine system serving as fuelproperties estimating apparatus according to a first embodiment of thepresent invention.

FIG. 2 is a flowchart showing a fuel properties estimating processaccording to the first embodiment.

FIG. 3 is a graph showing a characteristic of an estimated alcoholconcentration ALC and an air-fuel ratio sensitivity correction totalquantity αt, used in the process of FIG. 2.

FIG. 4 is a flowchart showing a fuel properties estimating processaccording to a second embodiment of the present invention.

FIG. 5 is a graph showing a characteristic of an ALC1 calculation mapused in the process of FIG. 4.

FIG. 6 is a graph showing a characteristic of an ALC2 calculation maphaving dead bands, used in the process of FIG. 4.

FIG. 7 is a graph showing a characteristic of an ALC2 calculation maphaving three dead bands, which can be used in the process of FIG. 4, inplace of FIG. 6.

FIG. 8 is a flowchart showing a fuel properties estimating processaccording to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an engine system, serving as fuel properties (composition)estimating apparatus, according to a first embodiment of the presentinvention. An engine in this example is of a type capable of using afuel containing alcohol.

An engine main block 1 includes at least one combustion chamber 2 withwhich an intake passage 4 is connected through an intake valve 3, and anexhaust passage 6 is connected through an exhaust valve 5.

In intake passage 4, there are provided an air cleaner 7, an airflowmeter 8 for sensing an intake air quantity, a throttle valve 9 forregulating the intake air quantity, and a fuel injector 11 for injectingfuel in the intake air.

An engine control unit (ECU) 12 produces a fuel injection commandsignal, and commands fuel injector 11 to inject fuel into the intake airto achieve a desired air-fuel ratio in accordance with engine operatingconditions.

In exhaust passage 6, there are provided an oxygen sensor 13 for sensingan oxygen concentration in the exhaust gas mixture, and a three-waycatalyst 14. Oxygen sensor 13 serves as air-fuel ratio sensing means forenabling calculation of an exhaust air-fuel ratio.

Three-way catalyst 14 can convert harmful emissions of hydrocarbons(HC), carbon monoxide (CO), and oxides of nitrogen (NOx) into lessharmful gases with a maximum conversion efficiency in a window of theair-fuel ratio around the stoichiometry. Therefore, ECU 12 controls theair-fuel ratio of the engine in a feedback control mode based on theoutput of oxygen sensor 13 located on the upstream side of three-waycatalyst 14 so that the actual air-fuel ratio swings periodically withinthe air fuel ratio window.

A water temperature sensor 15 senses the temperature of an enginecooling water in engine main block 1. ECU 12 is connected with thissensor, and arranged to receive information from this sensor.

Fuel containing alcohol requires a large amount of fuel injection ascompared to ordinary gasoline to obtain a given equivalence ratiobecause of the number of atoms of C (carbon), so that adjustment of thefuel injection quantity is required. Therefore, the engine system isarranged to predict the alcohol concentration of fuel accurately asquickly as possible, by utilizing the output signal of oxygenconcentration sensor 13. In this embodiment, alcohol is a component infuel, and the alcohol concentration is a component concentrationestimated by the system.

According to the first embodiment, the engine system estimates thealcohol concentration in the fuel, as a single component concentrationby following a process shown in FIG. 2.

Step S1 reads an air-fuel ratio feedback coefficient α (as an air-fuelratio correction quantity) calculated from the output of oxygenconcentration sensor 13.

Step S2 examines whether an air-fuel ratio learning condition issatisfied or not. When the learning condition is satisfied, the processproceeds to step S3, rewrites a map value in an αm calculation map foreach operating region at S3, and then proceeds to step S4. When thelearning condition is not satisfied, the process proceeds directly to S4without performing the map rewriting operation of S3. In this example,αm is an air-fuel ratio learning correction coefficient (as the air-fuelratio correction quantity). The air-fuel ratio feedback correctioncoefficient α and air-fuel ratio learning correction coefficient αm areparameters used for the feedback air-fuel ratio control. The fuelinjection quantity is corrected in accordance with the air-fuel ratiofeedback correction coefficient α and air-fuel ratio learning correctioncoefficient αm. This embodiment can employ various known methods forcalculating the air-fuel ratio feedback correction coefficient α andair-fuel ratio learning correction coefficient αm.

Step S4 determines a value of αm in each operating region by lookup inthe current αm map for each operating region.

Step S5 examines whether a fuel system for the engine is in a normalstate. If there is a failure in the fuel system including oxygen sensor13, air flowmeter 8, fuel injectors 11, water temperature sensor 15 anda canister purge system (not shown), then the program proceeds from S5to S6. Step S6 fixes an estimated alcohol concentration ALC at aprovisional value (40%) to prevent improper estimation of alcoholconcentration, and to enable restart of the engine and sustenance ofengine rotation after a start.

In this example, the provisional value in S6 is 40% which isintermediate between E85 fuel (ethanol concentration =85%) and E0 fuel(ethanol concentration=0). However, the provisional value is not limitedto 40%.

When there is no failure in the devices in the fuel system, the programproceeds from S5 to S7 to examine whether an estimation permittingcondition is satisfied or not. In this example, step S7 checks theengine cooling water temperature, elapsed time from a start of theengine, progress of the air-fuel ratio learning control, and history ofrefueling to determine whether the estimation permitting condition issatisfied. When the estimation permitting condition is satisfied, theprogram proceeds from S7 to S8. If the estimation permitting conditionis not satisfied, the program ends without performing the alcoholconcentration estimation.

Step S8 calculates an air-fuel ratio sensitivity correction totalquantity αt from the air-fuel ratio feedback coefficient α, air-fuellearning correction coefficient αm and a quantity ETAHOS, according tothe following equation.αt=α×αm′×ETAHOS  (1)Quantity ETAHOS is a fuel properties correction quantity determined froma previous value (most recent value) of the estimated alcoholconcentration ALC which is currently stored as ALC. In this example,fuel properties correction quantity ETAHOS is a previous value ofair-fuel ratio sensitivity correction total quantity αt calculated fromthe stored most recent value of ALC inversely by using a map of FIG. 3.

In the equation (1), αm′ is an average of αm values in representativespeed load regions. In this example, the average αm′ of αm is determinedfrom the αm values of four speed load regions. It is desirable toselect, as the representative four regions, regions which are usedrelatively frequently by the engine.

Step S9 calculates a new value of the estimated alcohol concentrationALC from the air-fuel ratio sensitivity correction total quantity αtcalculated at S8, by using the map shown in FIG. 3. The new value ofestimated alcohol concentration ALC calculated at S9 is stored in placeof the most recent value in a memory section in ECU 12 until nextcalculation of ALC at S9.

In the example shown in FIG. 3, the estimated alcohol concentration ALCvaries continuously with the air-fuel ratio sensitivity correction totalquantity αt, to achieve correction of the fuel injection quantity inaccordance with a deviation of the actual air-fuel ratio calculated fromthe output of oxygen sensor 13 from a target air-fuel ratio, to controlthe actual air-fuel ratio at or near the stoichiometric ratio. In aregion (of αt≧100%) in which the air-fuel ratio is on the lean side withrespect to the stoichiometric air-fuel ratio, the alcohol concentrationALC of this is increased linearly substantially in proportion to theair-fuel ratio sensitivity correction total quantity αt, as shown inFIG. 3. In a region (of αt<100%) in which the air-fuel ratio is on therich side with respect to the stoichiometric air-fuel ratio, theestimated alcohol concentration ALC is equal to 0%. In the example ofFIG. 3, the estimated alcohol concentration ALC is 0% when αt=100%; andALC is 85% when αt=140%.

The fuel properties estimating apparatus of the illustrated exampleincludes at least an air-fuel ratio correction quantity calculatingmeans corresponding to S1˜S4 of FIG. 3; a fuel system device failuredetecting means corresponding to S5; a provisional componentconcentration estimating means corresponding to S6; a fuel propertiescorrection quantity calculating means corresponding to S8; an air-fuelratio sensitivity correction total quantity calculating meanscorresponding to S8; and a nonprovisional component concentrationestimating means corresponding to S9.

The thus-constructed fuel properties estimating system determines a newvalue of the estimated component concentration of a component such asalcohol in fuel, by using the fuel properties correction quantity ETAHOSbased on a previous value of the estimated component concentration ALC,the air-fuel ratio feedback coefficient α, and the air-fuel learningcorrection coefficient αm. Therefore, the estimating system can reducean error of the estimated component concentration from the actualconcentration rapidly, and achieve accurate estimation of a componentconcentration for accurate combustion control to minimize deteriorationof exhaust performance and drivability. The quick estimation ofcomponent concentration according to this embodiment makes it possibleto produce a quick responsive control action such as an action to stopoperation to minimize engine performance deterioration.

In the case of failure of one of the fuel system devices, the estimatingsystem fixes the estimated component concentration ALC at thepredetermined (provisional) value (40%), and thereby prevents incorrectestimation. By using the provisional concentration value set at a levelenabling a start of the engine, the estimating system can prevent thevehicle from becoming unable to start because of errors in theestimation of alcohol concentration ALC. In this example, by employingthe provisional value (40%) intermediate between ethanol concentrationof 85% of E85 fuel and ethanol concentration of 0% of E0 fuel, thevehicle can start even if the actual fuel is E85 or E0.

The air-fuel ratio correction quantity includes the air-fuel ratiofeedback correction coefficient α. Therefore, the estimating system candetect concentration changes and transient state due to fuel stirringafter fueling, and fuel transportation delay in fuel piping.

Moreover, the air-fuel ratio correction quantity includes the air-fuelratio learning correction coefficient αm. Therefore, the estimatingsystem can reduce errors when fuel of the same alcohol concentration isused for a long period of time.

In the illustrated example, the air-fuel ratio sensitivity correctiontotal quantity αt is calculated from air-fuel ratio feedback correctioncoefficient α and air-fuel ratio learning correction coefficient αm′,both. However, it is optional to use either of α and αm′, as shown inthe following equation (2) or (3).αt=α×ETAHOS  (2)αt=αm′×ETAHOS  (3)The equation (2) including only α is obtained by setting αm′ to one inthe before-mentioned equation (1). Equation (3) including only αm′ isobtained by setting a to one.

FIGS. 4, 5, 6 and 7 show a second embodiment of the present invention.An engine system serving as fuel properties estimating apparatusaccording to the second embodiment is substantially identical inconstruction to the engine system shown in FIG. 1. FIG. 4 shows a fuelproperties estimating process performed by the system according to thesecond embodiment.

Steps S1˜S4 and S7˜S9 in FIG. 4 are substantially identical,respectively, to S1˜S4, and S7˜S9 of FIG. 2. In the example of FIG. 4,steps S5 and S6 of FIG. 2 are eliminated.

Step S9 of FIG. 4 is to determine a new value of a first estimatedalcohol concentration ALC1 from the air-fuel ratio sensitivitycorrection total quantity αt calculated at S8, by using an ALC1calculation map shown in FIG. 5 in the same manner as in S9 of FIG. 2and FIG. 3. The new value of estimated alcohol concentration ALC1calculated at S9 is saved in place of the most recent value of ALC1 inthe memory section in ECU 12 until next calculation of ALC1 at S9.

In the example shown in FIG. 5, the estimated alcohol concentration ALC1increases linearly with the air-fuel ratio sensitivity correction totalquantity αt, as in FIG. 3, in the region (αt≧100%) in which the air-fuelratio is on the lean side with respect to the stoichiometric air-fuelratio. In the region (αt<100%) in which the air-fuel ratio is on therich side with respect to the stoichiometric air-fuel ratio, theestimated alcohol concentration ALC1 is invariably equal to 0%. In theexample of FIG. 5, the first estimated alcohol concentration ALC1 is 0%(E0) when αt=100%; and ALC1 is 85% (E85) when αt=140%.

Step S28 follows S9, as shown in FIG. 4. Step S28 calculates a new valueof a second estimated alcohol concentration ALC2 from the firstestimated alcohol concentration ALC1 calculated at S9, by using an ALC2calculation map shown in FIG. 6. The new value of second estimatedalcohol concentration ALC2 calculated at S28 is stored as ALC2, in thememory section in ECU 12 until next calculation of ALC2 at S28. Step S28corresponds to means for estimating a second component concentrationALC2, or for calculating a second estimated component concentrationALC2.

This ALC2 calculation map of FIG. 6 is a characteristic for calculatingALC2 from ALC1, and this characteristic of ALC2 has at least one deadband with respect to ALC1. In other words, the ALC2 calculation map hasthe dead band in which second alcohol concentration ALC2 issubstantially constant regardless of changes in the air-fuel ratiosensitivity correction total quantity. The dead band is provided in apredetermined region of the air-fuel ratio sensitivity correction totalquantity on a lean side on which the exhaust air-fuel ratio is lean withrespect to the stoichiometric air-fuel ratio. In the example shown inFIG. 6, second estimated alcohol concentration ALC2 is invariably equalto 0% in a region of first estimated alcohol concentration ALC1 from 0%to 30%, and ALC2 is invariably equal to 85% in a region of firstestimated alcohol concentration ALC1 from 65% to 85%.

This characteristic of FIG. 6 is set to provide stable control values(control constants) when gasoline (E0 fuel having ethanol concentrationof 0%) is used or when standardized blend fuel (gasoline-alcohol blendfuel) such as E85 fuel having ethanol concentration of 85% is used. Theabove-mentioned control values (control constants) includes at least oneof control constant about the ignition timing, constant about correctionof wall flow of fuel, constant about cold enrichment, and constant aboutternary point adjustment of lambda control or a target air-fuel ratio inthe air-fuel ratio control. When these quantities are varied, therepeatability of emission control becomes worse. The problem can besolved by the setting of the dead band.

The ALC2 calculation map of this example includes a dead band at or nearthe ethanol concentration of E0 fuel, and a dead band at or near theethanol concentration of E85, both available on the market. Therefore,the result (ALC2) of estimation corresponds stably to the alcoholconcentration of a commercially available fuel within a limited range ofthe air-fuel ratio sensitivity correction quantity αt.

By calculating a plurality of estimated alcohol concentrations such asALC1 and ALC2, the estimating system can provide results of estimationadequate for respective different combustion parameters. First estimatedalcohol concentration ALC1 can be used for combustion parametersrequiring accurate adjustment based on an alcohol concentration in fuel.Second estimated alcohol concentration ALC2 can be used for combustionparameters, such as wall flow correction quantity, cold enrichmentquantity, target air-fuel ratio and ignition timing, requiring stableperformance for commercially available fuel, or guarantee of deviationof estimated concentration with respect to actual concentration.

The thus-constructed fuel properties estimating system according to thesecond embodiment determines a new value of first estimated componentconcentration ALC1 of a component such as alcohol in fuel, by using thefuel properties correction quantity ETAHOS based on a previous value ofthe estimated component concentration ALC1, the air-fuel ratio feedbackcoefficient α, and the air-fuel learning correction coefficient αm, asin the first embodiment. Therefore, the estimating system can reduce anerror of the estimated component concentration from the actualconcentration rapidly, and achieve accurate estimation of a componentconcentration for accurate combustion control to minimize deteriorationof exhaust performance and drivability.

The air-fuel ratio correction quantity includes the air-fuel ratiofeedback correction coefficient α, as in the first embodiment.Therefore, the estimating system can detect concentration changes andtransient state due to fuel stirring after fueling, and fueltransportation delay in fuel piping. Moreover, the air-fuel ratiocorrection quantity includes the air-fuel ratio learning correctioncoefficient αm, as in the first embodiment. Therefore, the estimatingsystem can reduce errors when fuel of the same alcohol concentration isused for a long period of time. In the second embodiment, too, it isoptional to use either of α and αm′, as shown in the equation (2) or(3).

In the example of FIG. 6, the ALC2 calculation map includes two deadbands. Instead, it is optional to employ an ALC2 calculation map havingthree dead bands as shown in FIG. 7. In the example of FIG. 7, thesecond estimated alcohol concentration ALC2 is set invariably equal to0% in an ALC1 region of ALC1 of 0%˜30%; invariably equal to 40% in aALC1 region of 35%˜45%; and invariably equal to 85% in an ALC1 region of65%˜85%.

FIG. 8 shows a third embodiment of the present invention. An enginesystem serving as fuel properties estimating apparatus according to thethird embodiment is substantially identical in construction to theengine system shown in FIG. 1. FIG. 8 shows a fuel properties estimatingprocess performed by the system according to the third embodiment.

Steps S1˜S4 and S7˜S9 in FIG. 8 are substantially identical,respectively, to S1˜S4, and S7˜S9 of FIG. 1 and FIG. 4. Step S28 issubstantially identical to S28 of FIG. 4. In FIG. 8, steps S31˜S33 areadded to the process of FIG. 4.

Step S1 calculates air-fuel ratio feedback coefficient α from the outputof oxygen concentration sensor 13 or ascertains the calculated air-fuelratio feedback coefficient. Step S2 examines whether the air-fuel ratiolearning condition is satisfied or not. Step S3 rewrites a map value inthe αm calculation map. When the learning condition is not satisfied,the process proceeds directly to S4. Step S4 determines air-fuel ratiolearning correction coefficient αm, as in the preceding embodiments. Theair-fuel ratio feedback correction coefficient α and air-fuel ratiolearning correction coefficient αm are air-fuel ratio correctionquantities used for the feedback air-fuel ratio control.

After S4, step S7 examines whether a normal estimation permittingcondition is satisfied or not. In this example, it is examined whether adisturbance affecting the exhaust air-fuel ratio is present or not. StepS7 of this examples checks the engine cooling water temperature, elapsedtime from a start of the engine, progress of the air-fuel ratio learningcontrol, and history of refueling to determine whether the estimationpermitting condition is satisfied. Moreover, step S7 of this examplechecks whether a quantity of blowby gases is smaller than or equal to apredetermined value. When the estimation permitting condition issatisfied, the program proceeds from S7 to S8. If the estimationpermitting condition is not satisfied, the program proceeds from S7 tostep 31.

Step S8 calculates the air-fuel ratio sensitivity correction totalquantity αt from air-fuel ratio feedback coefficient α, air-fuellearning correction coefficient αm and fuel properties correctionquantity ETAHOS, according to the equation (1), as in the precedingembodiments. Step S9 calculates a new value of the first estimatedalcohol concentration ALC1 from the air-fuel ratio sensitivitycorrection total quantity αt calculated at S8, by using the ALC1calculation map shown in FIG. 5, as in the preceding embodiments. Inthis example, first estimated alcohol concentration ALC1 is used forcorrecting the base fuel injection quantity (calculated from a sensedengine speed and a sensed intake air quantity).

After S9, step S28 calculates a new value of second estimated alcoholconcentration ALC2 from first estimated alcohol concentration ALC1calculated at S9, by using ALC2 calculation map shown in FIG. 6, as inthe second embodiment.

When the normal permitting condition is not satisfied, the programproceeds from S7 to step S31 corresponding to second permittingcondition discriminating means. Step S31 examines whether the air-fuelratio feedback correction coefficient α calculated at S1 is within apredetermined range, which, in this example, is 85%˜125%. The processproceeds to step S32 when air-fuel ratio feedback correction coefficientα is outside the range of 85%˜125%. When air-fuel ratio feedbackcorrection coefficient α is greater than or equal to 85% (0.85) andsmaller than or equal to 125% (1.25), then the process ends withoutperforming the estimation of alcohol concentration. In this case, thenormal permitting condition is so set that the normal permittingcondition is not satisfied when the air-fuel ratio feedback correctioncoefficient α is outside the range of 85%˜125%.

When 85%≦α≦125%, and hence the answer of S31 is YES, the engine systemuses the first and second estimated alcohol concentrations ALC1 and ALC2for engine control without updating ALC1 and ALC2.

Step S32 calculates the air-fuel ratio sensitivity correction totalquantity αt from the air-fuel ratio feedback coefficient α, air-fuellearning correction coefficient αm and a quantity ETAHOS, according tothe equation (1) as in S8.

Step S33 calculates a new value of the first estimated alcoholconcentration ALC1 from the air-fuel ratio sensitivity correction totalquantity αt calculated at S32, by using the ALC1 calculation map shownin FIG. 5. The new value of first estimated alcohol concentration ALC1calculated at S33 is stored in place of the most recent value in thememory section in ECU 12. In this case, the estimating system updatesonly the first estimated alcohol concentration ALC1. The secondestimated alcohol concentration ALC2 is not updated, and held unchangedin the memory section.

In this example, first estimated alcohol concentration ALC1 obtained atS33 is used for correcting the base fuel injection quantity. Firstestimated alcohol concentration ALC1 obtained at S9 is saved in thememory section until a new value of ALC1 is calculated by a nextoperation of S9 or S33. Second estimated alcohol concentration ALC1obtained at S28 is saved in the memory section until a new value of ALC2is calculated by a next operation of S28.

The estimating system according to the third embodiment calculates andupdates both the first and second estimated alcohol concentrations ALC1and ALC2 when the normal permitting condition of S7 is satisfied; andcalculates and updates only the first estimated alcohol concentrationALC1 when the estimation is permitted at S31. Second estimated alcoholconcentration ALC2 is not updated when the normal permitting conditionof S7 is not satisfied, even if the permitting condition of S31 issatisfied.

The estimated alcohol concentration stored in ECU 12 deviates largelyfrom the actual alcohol concentration in a fuel tank, for example,immediately after replenishment of fuel. In such a case, the estimatingsystem of the third embodiment calculates and updates the firstestimated alcohol concentration ALC1 even if the normal permittingcondition of S7 is not satisfied because of existence of disturbance tothe estimation. Therefore, the engine system can correct the base fuelinjection quantity accurately with first estimated alcohol concentrationALC1. The engine system can avoid insufficiency in control quantity inair-fuel ratio feedback control; and prevent deterioration of drivingperformance and exhaust performance by preventing over-lean conditionand over-rich condition in a combustion chamber.

Second estimated alcohol concentration ALC2 is not updated in theprogram section of S31˜S33. By updating second estimated alcoholconcentration ALC2 only in a reliable condition in this way, theestimating system can provide adequate value of ALC2 adequate for theintended purpose of ALC2.

A fuel properties estimating apparatus according to one aspect of theinvention comprises: a component concentration estimating controller tocalculate an air-fuel correction quantity for correcting a fuelinjection quantity for the engine, in accordance with an actual air fuelratio of the engine; to calculate a fuel properties correction quantityin accordance with a most recent value of the component concentration;to calculate an air-fuel ratio sensitivity correction quantity from theair-fuel ratio correction quantity and the fuel properties correctionquantity; and to calculate a new value of the estimated componentconcentration in accordance with the air-fuel ratio sensitivitycorrection quantity.

A fuel properties estimating apparatus according to another aspect ofthe invention comprises: an air-fuel ratio sensor to sense an actualexhaust air-fuel ratio of the engine; and a controller to determine anestimated component concentration of a component in a fuel for theengine in accordance with a control parameter determined from the actualexhaust air-fuel ratio, the controller being configured to determine theestimated component concentration with a dead band to hold the estimatedcomponent concentration substantially constant without regard tovariation in the control parameter in a predetermined region of thecontrol parameter

A fuel properties estimating apparatus according to still another aspectof the present invention comprises: an air-fuel ratio sensor to sense anactual exhaust air-fuel ratio of the engine; and a controller todetermine an estimated component concentration of a component in a fuelfor the engine in accordance with the actual exhaust air-fuel ratio, thecontroller being configured to calculate an air-fuel correction quantityfor correcting a fuel supply quantity for the engine, in accordance withthe actual air fuel ratio of the engine; to examine whether the air-fuelratio correction quantity is outside a predetermined region; and todetermine the estimated component quantity when the air-fuel ratiocorrection quantity is outside the predetermined region.

This application is based on a prior Japanese Patent Application No.2003-34444 filed on Feb. 13, 2003; a prior Japanese Patent ApplicationNo. 2003-34445 filed on Feb. 13, 2003; and a prior Japanese PatentApplication No. 2003-81804 filed on Mar. 25, 2003. The entire contentsof these Japanese Patent Applications are hereby incorporated byreference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. A fuel properties estimating apparatus for an internal combustionengine, the fuel properties estimating apparatus comprising: acontroller to determine an estimated component concentration of acomponent in a fuel for the engine, the controller being configured, tocalculate an air-fuel correction quantity for correcting a fuel supplyquantity for the engine, in accordance with an actual air fuel ratio ofthe engine; to calculate a fuel properties correction quantity inaccordance with a most recent value of the component concentration; tocalculate an air-fuel ratio sensitivity correction quantity from theair-fuel ratio correction quantity and the fuel properties correctionquantity; and to calculate a new value of the estimated componentconcentration in accordance with the air-fuel ratio sensitivitycorrection quantity.
 2. The fuel properties estimating apparatus asclaimed in claim 1, wherein the air-fuel correction quantity comprisesan air-fuel ratio feedback correction coefficient calculated inaccordance with the actual air fuel ratio sensed by an air-fuel ratiosensor.
 3. The fuel properties estimating apparatus as claimed in claim1, wherein the air-fuel correction quantity comprises an air-fuel ratiolearning correction quantity calculated in accordance with the actualair fuel ratio.
 4. The fuel properties estimating apparatus as claimedin claim 1, wherein the controller is configured to detect a failure ofa fuel system for the engine, and to set the estimated componentconcentration at a provisional fixed value when a failure in the fuelsystem is detected.
 5. The fuel properties estimating apparatus asclaimed in claim 1, wherein the controller is configured to increase theestimated component concentration in proportion to the air-fuel ratiosensitivity correction quantity when the actual air-fuel ratio is on alean side with respect to a stoichiometric ratio.
 6. The fuel propertiesestimating apparatus as claimed in claim 1, wherein the controller isconfigured to hold the estimated component concentration substantiallyconstant without regard to variation in the air-fuel ratio sensitivitycorrection quantity in a predetermined region of the air fuel ratiosensitivity correction quantity on a lean side of the actual air-fuelratio with respect to a stoichiometric ratio.
 7. The fuel propertiesestimating apparatus as claimed in claim 6, wherein the controller isconfigured to determine the estimated component concentration with adead band to hold the estimated component concentration substantiallyconstant without regard to variation in the air-fuel ratio sensitivitycorrection quantity in the predetermined region conform to acommercially available blend fuel.
 8. The fuel properties estimatingapparatus as claimed in claim 6, wherein the controller is configured todetermine a first component concentration and a second componentconcentration as the estimated component concentration in accordancewith the air-fuel ratio sensitivity correction quantity; to increase thefirst component concentration in proportion to the air-fuel ratiosensitivity correction quantity; and to determine the second componentconcentration with a dead band to hold the second componentconcentration substantially constant without regard to variation in theair-fuel ratio sensitivity correction quantity in the predeterminedregion of the air fuel ratio sensitivity correction quantity.
 9. Thefuel properties estimating apparatus as claimed in claim 8, wherein thecontroller is configured to use the first component concentration forcontrol of a first combustion parameter of the engine, and the secondcomponent concentration for control of a second combustion parameter ofthe engine.
 10. The fuel properties estimating apparatus as claimed inclaim 9, wherein the second combustion parameter is one of a wall flowcorrection, a cold enrichment quantity, a target air-fuel ratio and anignition timing.
 11. The fuel properties estimating apparatus as claimedin claim 9, wherein the first combustion parameter is a basic fuelinjection quantity for the engine.
 12. The fuel properties estimatingapparatus as claimed in claim 1, wherein the controller is configured toexamine whether the air-fuel ratio correction quantity is outside apredetermined region; and to determine the estimated component quantitywhen the air-fuel ratio correction quantity is outside the predeterminedregion.
 13. The fuel properties estimating apparatus as claimed in claim12, wherein the controller is configured to examine an engine operatingcondition to determine whether a first permitting condition issatisfied; to determine that a second permitting condition is satisfiedwhen the air-fuel ratio correction quantity is outside the predeterminedregion; and to refrain from calculating a new value of the estimatedcomponent concentration when the first permitting condition is notsatisfied and at the same time the second permitting condition is notsatisfied.
 14. The fuel properties estimating apparatus as claimed inclaim 13, wherein the controller is configured to determine a firstcomponent concentration and a second component concentration as theestimated component concentration in accordance with the air-fuel ratiosensitivity correction quantity; and the controller is furtherconfigured to determine new values of the first and second componentconcentrations when the first permitting condition is satisfied, and todetermine the new value of the first component concentration withoutdetermining a new value of the second component concentration when thefirst permitting condition is not satisfied and the second permittingcondition is satisfied.
 15. The fuel properties estimating apparatus asclaimed in claim 14, wherein the controller is configured to increasethe first component concentration in proportion to the air-fuel ratiosensitivity correction quantity; and to determine the second componentconcentration with a dead band to hold the second componentconcentration substantially constant without regard to variation in theair-fuel ratio sensitivity correction quantity in a predetermined regionof the air fuel ratio sensitivity correction quantity on a lean side ofthe actual air-fuel ratio with respect to a stoichiometric ratio. 16.The fuel properties estimating apparatus as claimed in claim 12, whereinthe controller is configured to conclude that the first permittingcondition is not satisfied when a disturbance exerting influence on anexhaust air-fuel ratio of the engine is present, and wherein thecontroller is configured to conclude that the disturbance is presentwhen a quantity of a blowby gas is greater than or equal to apredetermined value.
 17. The fuel properties estimating apparatus asclaimed in claim 12, wherein the controller is configured to examinewhether the air-fuel ratio correction quantity is outside thepredetermined region which is bounded between an upper limit greaterthan one and a lower limit smaller than one.
 18. The fuel propertiesestimating apparatus as claimed in claim 1, wherein the component in thefuel for the engine is alcohol.
 19. A fuel properties estimating processfor determining an estimated component concentration of a component in afuel for an internal combustion engine, the fuel properties estimatingprocess comprising: calculating an air-fuel correction quantity forcorrecting a fuel supply quantity for the engine, in accordance with anactual air fuel ratio of the engine; calculating a fuel propertiescorrection quantity in accordance with a most recent value of thecomponent concentration; calculating an air-fuel ratio sensitivitycorrection quantity from the air-fuel ratio correction quantity and thefuel properties correction quantity; and calculating a new value of theestimated component concentration in accordance with the air-fuel ratiosensitivity correction quantity.